Effects Of Climate And Land Use Changes On Runoff In Yarkant River Basin

Research on the impact of climate and land use changes on runoff is not only a hot issue in the related research of river basin hydrology,but also a problem with certain difficulties.This paper systematically collects data on hydrometeorology,land use,soil topography,glacier cataloging and climate models in the upper reaches of the Yarkant River,and analyzes the hydrological elements and land use change characteristics of the upper reaches of the Yarkant River in the past 50 years,such as precipitation,temperature and runoff;The study area is the headwater area of the upper reaches of the Yarkant River Basin.A SWAT hydrological model embedded with glacier modules was constructed.The monthly runoff from 1968 to 2017 at the Kaqun Hydrological Station was simulated.Through parameter sensitivity analysis,parameter calibration,model calibration and model analysis Applicability evaluation in the study area,localization of the SWAT model was completed,and a hydrological model suitable for the actual watershed situation in the upper reaches of the Yarkant River was constructed;based on the simulation results of the distributed hydrological model,the inter-annual variation and intra-year distribution of glacier runoff in the study area were analyzed and distinguished The impact of climate and land use changes on runoff changes and their contribution rates were quantitatively calculated;based on the future climate change model in the fifth phase of the coupled model comparison plan(CMIP5),the downscaling study of future meteorological elements with precipitation and temperature as the main factor was completed,Based on this,the established SWAT hydrological model is used to complete the simulation prediction of runoff evolution in the study area in the next 80 years.According to the main results of this research,we can understand the historical change trends of temperature,precipitation and runoff in the upper reaches of the Yarkant River,the response degree of runoff to climate and land use changes,and the future evolution trend of runoff in the river basin.Scientific management and further research.Main results are as follows:(1)In the past 50 years,the average annual precipitation in the study area has increased by39.8 mm,with an annual growth rate of 1.0%;the average annual temperature has risen by 2.44?,with an annual growth rate of 1.2%;the annual runoff has increased by 1.720 billion m~3,with an average annual growth rate of 0.5%;After the non-parametric statistical test,the precipitation,temperature and runoff series all passed the 95%significance test,indicating that the three have a significant increasing trend.The land use types in the study area are mainly bare rock land,grassland and glaciers,and the three land use types account for almost 96%of the entire basin.From 1990 to 2015,the single land use type in the upper reaches of the Yarkant River did not change much,and the structure was relatively stable.There are three main ways of transfer between land use types:glaciers to bare rock,low coverage grass to bare rock,and medium coverage grass to bare rock.The net transfer amounts are 786.2 km~2,221.1 km~2,and 65.7 km~2.(2)The applicability of the SWAT model with glacier module added to the runoff simulation of the upper Yarkant River is relatively good.The R2 of the calibration period(1968-1992)and the verification period(1993-2017)were 0.77 and 0.86,and the NSE was 0.76 and 0.85.RSR is 0.49and 0.38,and PBIAS is-7.4%and 0.6%.After simulation,the glacier runoff in the study area has been increasing over the years,and its proportion of the total runoff is about 51.1%;the glacier runoff mainly occurs from June to September during the year,accounting for more than 90%of the annual glacier runoff.(3)Changes in climate and underlying surface conditions increased monthly runoff by 6.62m~3·s-1 and 0.41 m~3·s-1,respectively.The contribution rates of climate and land use change were94.2%and 5.8%,respectively.Climate change and land use change And its coordinated changes will lead to an increase in monthly runoff in the source area of Yarkant River,and climate change will play a leading role in the evolution of runoff in the study area.(4)Under the three climate scenarios(RCP26/45/85),the temperature and precipitation in the upper reaches of the Yarkant River will increase from 2021 to 2100,but the significance of the increasing trend is different.The annual precipitation and daily average temperature increase more than the historical reference period.They are between 52.9%?68.3%and 1.24?3.31?respectively.Under different concentration paths,the simulated mean annual runoff decreased by0.21%,0.55%,and 1.06%respectively compared with the historical base period,and the annual runoff showed a significant decreasing trend under the RCP45/85 scenario.Under different climatic scenarios,the runoff in the upper reaches of the Yarkant River was generally relatively abundant in the first half of this century,and generally dry in the second half of this century,with an obvious turning point(roughly around 2050).The proportion of meltwater runoff increased slightly in the first half of this century,and its proportion decreased significantly in the second half of the century,showing a trend of first increasing and then decreasing;the contribution trend of rainfall runoff showed an overall increase,and the proportion increased.Stable,with small changes.